The present disclosure relates to a rotary electric machine control device that performs vector control on a rotary electric machine.
A control method called vector control is known as a control method for a permanent-magnet synchronous rotary electric machine, e.g. a three-phase synchronous motor. In the vector control, motor currents that flow through stator coils of the motor for three phases are subjected to a coordinate conversion into vector components for two phases, namely a d-axis, which extends in the direction of a magnetic field generated by a permanent magnet disposed in a rotor, and a q-axis, which is orthogonal to the d-axis, to perform feedback control. For the coordinate conversion, it is necessary to accurately detect the position of the rotor (magnetic pole position). In many cases, a rotation sensor such as a resolver is utilized to detect the magnetic pole position. For the purpose of cost reduction, however, sensorless magnetic pole detection in which the magnetic pole position is electrically detected on the basis of an electrical phenomenon that matches the magnetic pole position without using such a rotation sensor is occasionally performed. For example, an induced electromotive force produced by rotation of the rotor can be utilized to electrically detect the magnetic pole position. Because an induced electromotive force is not produced or only a small induced electromotive force is produced in the case where the rotor is stationary or in the case where the rotor is rotating at a very low speed, however, the magnetic pole position may not be detected accurately by the method. Thus, there is also proposed a method in which a high-frequency current or a high-frequency voltage is applied to a motor and the magnetic pole position is estimated in accordance with a response from the motor.
When it is attempted to decide the magnetic pole position (or the phase of a rotating d-q-axis coordinate system) by one of the method which utilizes an induced electromotive force and the method which applies a high frequency, that is, a single method, the accuracy is reduced in a high speed rotation range (a region in which the rotation frequency is high) or a low speed rotation range (a region in which the rotation frequency is low). Japanese Patent Application Publication No. H10-94298 (JP H10-94298 A) proposes a technology that addresses such an issue about sensorless magnetic pole detection. According to JP H10-94298 A, two phase decision methods, namely a phase decision method for a low frequency region and a phase decision method for a high frequency region, are used to generate phases, and the two phases are weight-averaged with respect to the frequency to obtain the phase of a d-q-axis coordinate system.
By applying the technology according to JP H10-94298 A, the phase is decided on the basis of a method that is suitable for the rotation frequency, among the two methods, by weight-averaging the two phases with respect to the frequency to switch between the two phase decision methods at a certain ratio in accordance with the rotation frequency. In both the method used in the low frequency region (e.g. the method in which a high-frequency current or a high-frequency voltage is applied to the motor) and the method used in the high frequency region (e.g. the method which utilizes an induced electromotive force), however, the estimation accuracy in estimating the magnetic pole position tends to be varied in accordance with torque of the motor. Thus, a sufficient accuracy in deciding the phase (estimating the magnetic pole position) may not be secured only by switching the phase decision method and deciding the weight for weight averaging on the basis of the rotation frequency.